As a vehicle, there is a hybrid vehicle for driving and controlling a vehicle by using outputs from an internal combustion engine and a plurality of motor generators (electric motors) as drive sources.
As such a hybrid vehicle, there are a series system (the internal combustion engine is used only to rotate the power generator and the whole driving is performed by the motor generators) and a parallel system (the internal combustion engine and the motor generator are arranged in parallel and their motive powers are used for driving).
In the hybrid vehicle, as another system of the series system and the parallel system, there is such a system that as a power transmission mechanism of a triaxial type, a motive power of an internal combustion engine is divided to a power generator and a drive axis by using one planetary gear mechanism (differential gear mechanism having three rotational elements) and two motor generators (first motor generator: MG1, second motor generator: MG2) as a motor generator and the motor generator provided for a drive axis is driven by using an electric power generated by the power generator, thereby torque converting the motive power of the internal combustion engine (the Official Gazette of Japanese Patent No. 3050125, the Official Gazette of Japanese Patent No. 3050138, the Official Gazette of Japanese Patent No. 3050141, the Official Gazette of Japanese Patent No. 3097572).
Thus, in the hybrid vehicle, the operation point of the internal combustion engine (engine operation point) can be set to an arbitrary point where a stop is included and fuel consumption is improved.